1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets and a sub tank for supplying liquid to the recording head.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid ejection head or liquid-droplet ejection head) for ejecting droplets of ink or other liquid.
The sub tank may have a negative-pressure forming function (mechanism) to create a negative pressure to prevent ink from exuding or dropping from nozzles of the recording head. The sub tank has a negative-pressure forming unit and an air release unit. The negative-pressure forming unit includes a flexible member (film member) to form one face of an ink storage part to store ink and an elastic member to urge the flexible member outward. The air release unit is openably disposed at the sub tank to release the interior of the ink storage part to the atmosphere. Ink is supplied from the ink storage part to the recording head.
The sub tank has a displacement member (also referred to as detection member or detection feeler) to displace with the displacement of the flexible member. When ink is supplied from the main tank to the sub tank with the air release unit of the sub tank opened, i.e., air release filling is performed, the carriage is moved to a predetermined detection position (ink full position) and a driving device of the air release unit disposed at the apparatus body is activated to release the interior of the sub tank to the atmosphere. In such a state, ink filing is started. When a detector disposed at the apparatus body detects the displacement member, the position of the carriage is determined as the ink full position (see JP-2009-023092-A).
In such a case, to allow ink to be replenished and supplied during printing operation, if the consumption amount of ink during printing is a first threshold value or more and it is determined based on information associated with the amount of ink supplied from the main tank to the sub tank during printing that the amount of ink supplied is a second threshold value or less, ink is supplied from the main tank to the sub tank. By contrast, if the amount of ink supplied is greater than the second threshold value, ink is not supplied from the main tank to the sub tank.
Alternatively, instead of the above-described configuration, the sub tank may be provided with a detector for detecting the amount of ink remaining in the sub tank to allow ink supply during printing operation (see JP-3210326-B1 (JP-06-183027-A)).
For the above-described configuration in which the sub tank has the displacement member displaceable with the remaining amount of ink in the sub tank to allow detection of an ink full state of the sub tank, when ink is supplied from the main tank to the sub tank, the carriage need be moved to the predetermined ink full position. As a result, when the remaining amount of ink in the sub tank decreases below a threshold value during printing, the printing need be temporarily stopped for ink supply operation, thus reducing printing speed.
In such a case, for example, by counting the number of ink droplets ejected from the head, the consumption amount of ink in the sub tank may be calculated to supply ink from the main tank by a supply amount corresponding to the consumption amount. However, for such a configuration, since the ink full position is not accurately detected, insufficient ink supply might cause an excessive negative pressure or excessive ink supply might cause an insufficient negative pressure. For this reason, the carriage need be regularly moved to the ink-full detection position to perform the air release filling. As a result, printing operation need be stopped, thus reducing the printing speed.
In addition, it is conceivable to provide, with the carriage, a detector for detecting the remaining amount of ink in the sub tank, a driving device for driving the air release unit of the sub tank, and a member and/or device to control ink supply to the sub tank. However, such a configuration increases the size and weight of the carriage, thus resulting in an increased size of the entire apparatus.